Buy or borrow a cleaner, Rent one at the store, or call the boys in the truck?  They're not filthy but, it's time.

If you don't have any pets and don't really clean the carpets all that often, I would recommend calling the boys in the truck if you can afford it.  If not, just rent one at the store.  I own mine, but I spot clean a lot so I need to keep it handy.  The ones you rent from the store are much quicker and do a better job if you only need to clean them occasionally.  That's my .02.

My in-laws have a steam cleaner, so we just use that. I would either rent or buy, or borrow if you can.

I'd stay away from the boys in the truck. My brother is in the flooring business and said most of those services either aren't worth it or are sketchy.

Ask questions, whether an outside cleaner or a do-it-yourself machine, as to what the machine really does, how it works. I had new carpet installed recently, and the installer showed me that the backing on the new stuff (not cheap) was water soluble, while the old stuff was not. He said that all new carpet is like that. If you get enough water on it, it will start to come apart. Try it with a scrap of your carpet if you have one. Many "steam cleaners", rented or professional, are really hot water injection systems, that spray hot water and shampoo on the carpet and wet-vac it back up again. I don't think that any system will damage the carpet in one use if you don't let the water soak in, but you don't want to use any water-based system very often.

Amen to that.  With two unfixed girl dogs we use our steam cleaner quite a bit.  Just don't expect too much.  It will brighten the carpet and clean some dirt but it will not remove stains.  In fact we have a couple water stains from cleaning up some rather large pet messes.
Borrow or rent, but don't do it too often.

Ratters...I had the same problem with the water stains when I got a bit overly zealous trying to clean up a pet mess.  You don't want to saturate the carpet and pad when you clean.  It just brings all the dirt out of the pad up into the carpet where it's visible.  I found a solution, though.  Get some Resolve.  Spray the stained area and let it sit for a couple of hours.  Then go over the area with your steam cleaner again.  It worked great for me, and I have light beige carpet.  Good luck to all.